Magnetic properties of Ruddlesden-Popper phases Sr3−x_{3-x}Yx_{x}(Fe1.25_{1.25}Ni0.75_{0.75})O7−δ_{7-\delta}: A combined experimental and theoretical investigation

We present a comprehensive study of the magnetic properties of Sr$_{3-x}$Y$_{x}$(Fe$_{1.25}$Ni$_{0.75}$)O$_{7-\delta}$ ($0 \leq x \leq 0.75$). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by the theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the N\'eel temperature ($T_N$) with the increase of Y concentrations and O occupancy. The NPD data reveals all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the 3D magnetic order is stabilized due to finite inter-layer exchange couplings. The latter give rise to a finite inter-layer spin correlations which disappear above the $T_N$

Influence of the presence of different alkali cations and the amount of Fe(CN)6 vacancies on CO2 adsorption on copper hexacyanoferrates

The CO2 adsorption on various Prussian blue analogue hexacyanoferrates was evaluated by thermogravimetric analysis. Compositions of prepared phases were verified by energydispersive X-ray spectroscopy, infra-red spectroscopy and powder X-ray diffraction. The influence of different alkali cations in the cubic Fm3m structures was investigated for nominal compositions A2/3Cu[Fe(CN)6]2/3 with A = vacant, Li, Na, K, Rb, Cs. The Rb and Cs compounds show the highest CO2 adsorption per unit cell, ~3.3 molecules of CO2 at 20 \ub0C and 1 bar, while in terms of mmol/g the Na compound exhibits the highest adsorption capability, ~3.8 mmol/g at 20 \ub0C and 1 bar. The fastest adsorption/desorption is exhibited by the A-cation free compound and the Li compound. The influence of the amount of Fe(CN)6 vacancies were assessed by determining the CO2 adsorption capabilities of Cu[Fe(CN)6]1/2 (Fm3m symmetry, nominally 50% vacancies), KCu[Fe(CN)6]3/4 (Fm3m symmetry, nominally 25% vacancies), and CsCu[Fe(CN)6] (I-4m2 symmetry, nominally 0% vacancies). Higher adsorption was, as expected, shown on compounds with higher vacancy concentrations

Oxygen-deficient perovskite-related (Nd0.4Sr0.6)2Ni0.8M0.2O4-δ as oxygen electrode materials for SOFC/SOEC

Perovskite-related Ln2NiO4+δ (Ln = La, Pr, Nd) nickelates with layered Ruddlesden-Popper combine redox stability with noticeable oxygen stoichiometry changes, yielding enhanced mixed transport and electrocatalytic properties. These unique features are promising for applications as oxygen electrodes with good electrochemical performance in reversible SOFC/SOEC (solid oxide fuel/electrolysis cell) systems. To date, most efforts were focused on oxygen-hyperstoichiometric Ln2NiO4+δ-based phases, whereas nickelates with oxygen-deficient lattice remain poorly explored. Recent studies demonstrated that the highest electrical conductivity in (Ln2-xSrx)2NiO4±δ series at elevated temperatures is observed for the compositions containing ~ 60 at.% of strontium in A sublattice [1,2]. The present work was focused on the characterization of (Nd0.4Sr0.6)2Ni0.8M0.2O4-δ (M = Ni, Co, Fe) nickelates for the possible use as materials for reversible oxygen electrodes. The ceramic materials were prepared by Pechini method with repeated annealings at 650-1200°C and sintered at 1250-1300°C for 5 h under oxygen atmosphere. Variable-temperature XRD studies confirmed that all studied compositions retain tetragonal K2NiF4-type structure in the temperature range 25-900°C. The results of thermogravimetric analysis showed that the prepared nickelates has oxygen-deficient lattice under oxidizing conditions at temperatures above 700°C. Partial substitution of nickel by cobalt or iron results in a decrease of p-type electronic conductivity and the concentration of oxygen vacancies in the lattice (Fig.1), but also suppresses dimensional changes associated with microcracking effects (due to anisotropic thermal expansion of tetragonal lattice). Electrochemical performance of porous (Nd0.4Sr0.6)2Ni0.8M0.2O4-δ electrodes in contact with Ce0.9Gd0.1O2-δ solid electrolyte was evaluated at 600- 800°C employing electrochemical impedance spectroscopy and steady-state polarization (anodic and cathodic) measurements.publishe

Synthesis, structure and dielectric properties of a new family of phases, ABC3O11 : A = La, Pr, Nd, Sm, Gd; B = Zr, Hf; C = Ta, Nb

Eight new phases with the general formula of ABC3O11 with different rare earth, (Zr, Hf), (Nb, Ta) combinations, have been prepared by solid-state reactions at a temperature range of 1200–1500 °C. The new phases—LaHfTa, LaHfNb, LaZrNb, PrHfTa, NdHfTa, NdHfNb, SmHfTa and GdHfTa—are characterised by X-ray and neutron diffraction data at room temperature and variable frequency impedance measurements. They are isostructural with LaZrTa3O11 which consist of alternating single layers of UO7 pentagonal bipyramids and octahedra as shown by Rietveld refinement of X-ray and neutron powder diffraction data. Lattice parameters decrease with decreasing size of rare earth element substitution at A-site, and of all, Gd is the smallest rare earth that formed LaZrTa3O11 analogues. Detailed attempts of attained and unattainable LaZrTa3O11 analogues with different temperatures are included in this paper. All phases are highly insulating with temperature-independent bulk permittivities in the range 17 to 50; LaHfNb demonstrates the highest permittivity. Arrhenius plot shows that the activation energies are in the range 0.8 to 1.94 eV

Oxygen-deficient Nd0.8Sr1.2Ni0.8M0.2O4-δ (M = Ni, Co, Fe) nickelates as oxygen electrode materials for SOFC/SOEC

Ruddlesden-Popper Nd0.8Sr1.2Ni0.8M0.2O4±δ (M = Ni, Co, Fe) nickelates have been characterized as prospective oxygen electrode materials for solid electrolyte cells. XRD studies showed that these oxides retain tetragonal K2NiF4-type structure in air until at least 900°C. Average thermal expansion coefficients of Nd0.8Sr1.2Ni0.8M0.2O4±δ calculated from the structural data are in the range 14.5-15.8 ppm/K. TGA studies revealed that these nickelates are oxygen-deficient in air at temperature above 700°C but tends to oxygen stoichiometry or minor excess on cooling. Incorporation of cobalt or iron into nickel sublattice of Nd0.8Sr1.2NiO4-δ reduces oxygen deficiency and electrical conductivity. Electrochemical impedance spectroscopy studies of symmetrical cells showed that porous Nd0.8Sr1.2Ni0.8M0.2O4-δ electrodes applied onto Ce0.9Gd0.1O2-δ electrolyte exhibit quite similar performance, with lowest values of polarization resistance (0.8 Ohm×cm2 at 800°C) observed for M = Ni. The polarization resistance can be further decreased (down to 0.04 Ohm×cm2 at 800°C for M = Ni) by surface modification with PrOx.publishe

ВЛИЯНИЕ МЕТОД А СПЕКАНИЯ НА МИКРОСТРУКТУРУ КЕРА МИКИ ND0,4SR1,6NIO

Two different methods have been employed for fabrication of Nd0.4Sr1.6NiO4–d ceramics with focus on the microstructure and density of ceramic samples. Conventional sintering at 1100–1300 °C has been found to yield porous materials. Rapid grain growth at ≥1 300 °C induces the development of microcracks associated with a strongly anisotropic expansion ofNd0.4Sr1.6NiO4–d tetragonal lattice. On the contrary, spark plasma sintering (SPS) at 1100 °C enables fabrication of dense gastight ceramics, but is accompanied by the structural transformation from tetragonal (I4/mmm) to orthorhombic (Immm) symmetry due to oxygen losses from the lattice under low-p(O2) conditions of SPS process. The post-treatment conditions were optimized to oxidize sintered samples and to restore tetragonal structure while preserving gas-tightness of ceramics.Исследовано влияние методов свободного спекания и плазменного искрового спекания (ПИС) на микроструктуру керамики Nd0,4Sr1,6NiO4–d. Установлено, что керамика, изготовленная свободным спеканием, является пористой независимо от температуры отжига. Керамика, полученная методом плазменного искрового спекания, – газоплот-ная. однако в результате применения восстановительной атмосферы вакуума в процессе ПИС происходит структурное превращение тетрагональной ячейки I4/mmm в орторомбическую Immm. В результате проведенной серии термообработок керамики были найдены оптимальные условия последующего отжига керамики, приводящие к восстановлению тетрагональной структуры оксида (Immm→I/4mmm) и сохранению газоплотности керамики Nd0,4Sr1,6NiO4–d

Spark plasma sintering of TiyNb1-yCxN1-x monolithic ceramics obtained by mechanically induced self-sustaining reaction

Nanometer-sized titanium-niobium carbonitride powders (TiyNb1-yCxN1-x) with different Ti/Nb atomic ratios were obtained by a mechanically induced self-sustaining reaction, and sintered by spark plasma sintering technique at 1500 degrees C for 1 min in a vacuum atmosphere. Mechanical properties such as hardness and Young's modulus were determined by nanoindentation technique and friction and wear coefficients assessed by ball-on-disk testing using alumina ball in dry sliding conditions. The fracture surface and wear tracks of samples were examined by scanning electron microscopy. Results showed that it is possible to obtain dense monolithic ceramics from the solid solution (TiyNb1-yCxN1-x) with good mechanical properties and excellent wear resistance. The optimum values of nanomechanical properties were found for the Ti0.3Nb0.7C0.5N0.5 ceramic composition, which exhibited a high hardness over 26.0 GPa and Young's modulus around 400 GPa. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.The authors would like to thank Dr. Emilio Rayon for performing the nanoindentation analysis in the Materials Technology institute (ITM) of the Polytechnic University of Valencia and to acknowledge the financial support received from Spanish Ministry of Science and Innovation for FPI grant (MAT2006-01783). This work was supported by the Spanish government under grant (MAT2010-17046), which is financed in part by the European Regional Development Fund of 2007-2013. E. Chicardi was supported by CSIC through a JAE-Pre grant, which is financed in part by the European Social Fund (ESF).Borrell Tomás, MA.; Salvador Moya, MD.; Garcia-Rocha, V.; Fernandez, A.; Chicardi, E.; Gotor, FJ. (2012). Spark plasma sintering of TiyNb1-yCxN1-x monolithic ceramics obtained by mechanically induced self-sustaining reaction. Materials Science and Engineering: A. 543:173-179. https://doi.org/10.1016/j.msea.2012.02.071S17317954

ТЕРМИЧЕСКОЕ РАСШИРЕНИЕ, ЭЛЕКТРИЧЕСКАЯ ПРОВОДИМОСТЬ И КИСЛОРОДНАЯ НЕСТЕХИОМЕТРИЯ НИКЕЛАТОВ La2-xSrxNiO4-δ КАК ПОТЕНЦИАЛЬНЫХ КАТОДНЫХ МАТЕРИАЛОВ TОТЭ

La2-xSrxNiO4-δ (x = 1.0–1.6) nickelates were evaluated as potential cathode materials for solid oxide fuel cells, with focus on the structural stability, oxygen nonstoichiometry and electrical conductivity under oxidizing conditions. All studied ceramic materials were found to preserve K2NiF4-type tetragonal structure under oxidizing conditions at 25–900  °С.La2-xSrxNiO4-δ (x = 1.0–1.6) nickelates demonstrate oxygen deficiency at temperatures above 500 °С, with oxygen nonstoichiometry increasing with temperature and strontium content. The electrical conductivity is p-type and show metallic-like behavior under oxidizing conditions at 500–1000 °С. The highest conductivity values, 220 S/cm at 900 °С and 440  S/cm at 600 °С in air, are measured for La0,8Sr1,2NiO4-δ ceramics. While the high-temperature XRD studies revealed strongly anisotropic thermal expansion of La2-xSrxNiO4-δ crystal lattice, the lattice volume show nearly linear dependence on temperature, with average linear thermal expansion coefficients varying in the range (14.2–15.6) · 10-6 K-1.Оксиды системы La2-xSrxNiO4-δ (x = 1,0–1,6) были исследованы в качестве  потенциальных катодных материалов для твердооксидных топливных элементов. Были изучены структурная стабильность, кислородная нестехиометрия и электрическая  проводимость. Установлено, что все оксиды сохраняют кристаллическую структуру типа K2NiF4 в окислительных условиях в температурной области 25–900 °С. Оксиды данной системы являются дефицитными по кислороду при температурах выше 500 °С, и  кислородная нестехиометрия повышается с ростом температуры и увеличением содержания стронция. Исследованные никелаты обладают псевдометаллической электропроводностью p-типа в окислительных условиях при температурах 500–1000 °С. Наибольшая электрическая проводимость характерна для La0,8Sr1,2NiO4-δ (220 См/см при 900 °С и 440 См/см при 600 °С). Методом высокотемпературной рентгеновской дифракции установлено, что никелаты La2-xSrxNiO4-δ проявляют анизотропное термическое расширение кристаллической решетки, однако объемное термическое расширение носит практически линейную зависимость от температуры; значения линейных коэффициентов термического расширения составляют (14,2–15,6) · 10-6 K-1

Can pulsed ultrasound increase tissue damage during ischemia? A study of the effects of ultrasound on infarcted and non-infarcted myocardium in anesthetized pigs

BACKGROUND: The same mechanisms by which ultrasound enhances thrombolysis are described in connection with non-beneficial effects of ultrasound. The present safety study was therefore designed to explore effects of beneficial ultrasound characteristics on the infarcted and non-infarcted myocardium. METHODS: In an open chest porcine model (n = 17), myocardial infarction was induced by ligating a coronary diagonal branch. Pulsed ultrasound of frequency 1 MHz and intensity 0.1 W/cm(2 )(I(SATA)) was applied during one hour to both infarcted and non-infarcted myocardial tissue. These ultrasound characteristics are similar to those used in studies of ultrasound enhanced thrombolysis. Using blinded assessment technique, myocardial damage was rated according to histopathological criteria. RESULTS: Infarcted myocardium exhibited a significant increase in damage score compared to non-infarcted myocardium: 6.2 ± 2.0 vs. 4.3 ± 1.5 (mean ± standard deviation), (p = 0.004). In the infarcted myocardium, ultrasound exposure yielded a further significant increase of damage scores: 8.1 ± 1.7 vs. 6.2 ± 2.0 (p = 0.027). CONCLUSION: Our results suggest an instantaneous additive effect on the ischemic damage in myocardial tissue when exposed to ultrasound of stated characteristics. The ultimate damage degree remains to be clarified